There has long been vehement opposition to the prospect of a gold mine and processing plant being built at Skouries in the Halkidiki peninsula, with residents objecting to what they say will be the destruction of the environment and of pristine forest in the area, leading to the loss of tourism and other local activities such as farming, the rearing of livestock and fishing.

The mining company, Hellas Gold, is 95% owned by Canadian mining company Eldorado Gold ( EGO). The Greek government has been eager for the foreign investment as it struggles through a deep financial crisis. But the dispute has led to frequent protests in the area, with tear gas and firebombs used and residents trading accusations with the company about heavy-handed reactions and the use of violence.

In Sunday's attack, firefighters and police said the intruders raided the facility after midnight, using gasoline bombs and flammable liquid to set alight machinery, vehicles and containers used as offices, causing extensive damage.

Police detained 27 people for questioning in a local police station early Sunday morning, they said. No arrests were immediately made. Authorities said one security guard employed by the company to guard the facilities sought treatment at a hospital after being kicked.

The Skouries project is the latest in a complex of mining facilities in the area. Hellas Gold -- mostly owned by Eldorado Gold and 5% owned by Greek construction company Aktor -- holds mining licenses for an area covering 317 square kilometers (122 square miles) with proven and probable reserves of lead, zinc, silver, gold and copper.

Many see the foreign investment as vital to helping Greece emerge from what is essentially a depression, with a quarter of the workforce unemployed and the economy heading into a sixth year of recession.

Opponents also argue that unlike many other countries, the Greek state gets no royalties from mine concessions, so stands to gain only taxes and jobs. Concessions granted in 2004 for Stratoni, one of the Halkidiki mines that is currently operating and is near Skouries, are valid until 2026 and can be renewed twice for 25 years each time, free of charge.